The present invention generally relates to rotary machines such as steam and gas turbines and, more particularly, to a rotary machine seal for controlling clearance between the shank portions of rotating rotor blades or “buckets” and radially inner ends of adjacent, stationary stator components.
Land-based steam and gas turbines are used, for example, to power electric generators. Gas turbines are also used, for example, to propel aircraft and ships. A steam turbine has a steam path which typically includes in serial-flow relation, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relation, an air intake or inlet, a compressor, a combustor, a turbine, and a gas outlet or exhaust nozzle. In both steam and gas turbines, compressor and turbine sections include at least one circumferential row of rotating blades or buckets mounted on rotor wheels or disks. The free ends or tips of the rotating buckets are surrounded by a stator casing. The base or shank portions of the respective rotating buckets within a row are typically provided with so-called “angel-wing” seals that are flanked by stationary stator components such as nozzle vanes or diaphragms disposed, respectively, upstream and downstream of the moving blades.
The efficiency of the turbine depends in part on the radial clearance or gap between the rotor bucket angel wing seal tip(s) and a sealing structure on the adjacent stationary stator component. If the clearance is too large, excessive and valuable cooling air will leak through the gap, decreasing the turbine's efficiency. If the clearance is too small, the angel wing tip(s) will strike the sealing structure of the adjacent stator component during certain turbine operating conditions, causing undesirable wear on both the angel wing tip(s) and the stationary stator component(s).
With respect to the radial clearance mentioned above, it is known that the clearance changes during periods of acceleration or deceleration due to changing centrifugal forces on the buckets; turbine rotor vibration; and relative thermal growth between the rotating rotor and the stationary stator components. During periods of differential centrifugal force, rotor vibration, and thermal growth, the clearance changes can result in severe rubbing of the rotating bucket angel wing seal tips against the stationary seal structures. Increasing the tip-to-seal clearance gap reduces the damage due to metal to metal rubbing, but the increase in clearance results in efficiency loss.
There remains a need for a seal construction that accommodates differential axial and radial movement of the rotor/bucket assembly and the adjacent stationary stator components but that does not negatively impact turbine performance.